The present invention relates to an apparatus for aligning electronic components and more particularly to an apparatus in which the position of a pattern on a printed board and the position of each lead of an electronic component are detected by optical means and the amount of deviation in position between the two is calculated from their picture data thereby correcting the deviation.
Some of apparatus heretofore known for performing the alignment operation required for mounting electronic components on a printed board (printed-circuit board) will now be described by way of example.
One of the known methods is designed so that after the leads of an electronic component have been preliminarily aligned with a gap over the conductor pattern of a horizontally arranged printed board, the operator corrects any positional deviation by moving the electronic component or the printed board while simultaneously observing visually the images of the pattern and the leads from just above through a magnifying glass or the like.
Another method is to preliminarily align the leads of an electronic component over the conductor pattern of a printed board in the same manner as mentioned above. Then, a picture is taken by a camera from just above the leads of the electronic component and the picture is reproduced on a television reciever. The operator corrects any positional deviations by moving the electronic component or the printed board while observing the picture of the leads against the pattern reproduced in enlarged form on the television screen instead of directly observing the images visually.
With the recent increase in electronic component lead density, however, there has been a need for a method capable of aligning an electronic component on a conductor pattern with greater accuracy and the above-mentioned methods of effecting the desired alignment by detecting the relative positional relation between a lead image and a pattern image through visual observation are disadvantageous from the standpoints of production efficiency and accuracy. Thus, there has existed a need for an automatic alignment apparatus.
Various types of automatic alignment apparatus using pattern recognition techniques have been developed. The following is an example of this type of apparatus. This apparatus first takes a picture of a pattern illuminated by a lamp by a first camera; then it preliminary aligns an electronic component held by a chuck over the pattern; then it takes a picture of the leads of the electronic component illuminated by a lamp by a second camera; and then it supplies the pictures taken by the cameras to a recognition device. In the recognition device, after the pictures of the pattern and the leads have each been converted to digital form and stored in a picture memory, the pictures in the memory are compared and positional deviation values are calculated. In this case, the reason for using the two cameras for photographing twice is that the simultaneous photographing of the pattern and the leads by one camera cannot ensure a satisfactory resolution for the pictures due to the gap between the pattern and the leads. It is to be noted that in this apparatus the reflected light from the pattern or the leads is detected from a direction perpendicular to the printed board and a half mirror or the like is used to branch and direct the vertical component of the reflected light to the two cameras.
However, a method of the kind which utilizes the reflected light from a pattern as in the case of the above-mentioned automatic alignment apparatus involves a substantial disadvantage. Namely, where the pattern is a solder pattern, the surface condition is not uniform and there are the variations in surface condition among individual sample of pattern. In other words, there is a disadvantage that since there are the variations in shape, surface luster, etc., among the different samples, the reflected light from the pattern is not stable and the binarization of picture information is not an easy matter. There is another problem that depending on the manner of illumination the surface of the printed board gleams thus making it difficult to distinguish the pattern from the printed board substrate.
The present invention has been made on the basis of an idea of utilizing the fluorescent light emitted from the substrate of a printed board, which occurred in the course of an investigation into any other method than the method of utilizing the reflected light from a pattern.